Transcript Volcanoes and Other Igneous Activity

화산과 화산활동
화산활동의 다양성
화산활동의 다양성 요인
• Three factors determine the
“violence” or explosiveness of a
volcanic eruption:
1. Composition of the magma
2. Temperature of the magma
3. Dissolved gases in the magma
점성도(Viscosity)
• These three factors control the viscosity
of a given magma, which in turn controls
the nature of an eruption.
• Viscosity is a measure of a material’s
resistance to flow.
– Higher viscosity materials flow with great
difficulty.
점성도 영향 요소
1. Temperature – Hotter magmas are less
viscous.
2. Composition – Silica (SiO2) content
–
Higher silica content = more SiO4
chains/structures = higher viscosity
•
–
felsic lava – rhyolite (유문암)
Lower silica content = fewer SiO4
chains/structures = lower viscosity or more
fluid like behavior
•
mafic lava – basalt (현무암)
점성도 영향 요소
3. Dissolved Gases (용존가스)
–
분출의 폭발성은 마그마로부터 얼마나
쉽게 가스가 분출할 수 있는 지에 따라
결정됨
–
–
Gas content affects magma mobility.
Volatiles migrate upward and accumulate near
the top of the magma chamber, enriching the
upper portion of the magma chamber with
dissolved gases.
Gases expand within a magma as it nears the
Earth’s surface due to decreasing pressure.
Escaping gases provide the force to propel molten
rock from the volcanic vent.
–
–
점성도 영향 요소
3. Dissolved Gases
–
–
Very fluid basaltic
magmas allow the
gases to migrate
upwards and escape
the vent with relative
ease.
Produces lava
fountains extending
hundreds of meters
in height.
점성도 영향 요소
3. Dissolved Gases
– Highly siliceous magmas
undergo magmatic
differentiation leaving the
upper portion of the magma
chamber enriched in silica
and dissolved gases.
– The volcano summit begins
to inflate and bulge months
to years prior to eruption.
– As the magma migrates up
the vent, the gases collect
into tiny bubbles.
– The mixture is transformed
into a gas jet containing tiny
magma fragments that are
explosively ejected.
– Produces plumes of a hot
ash-laden gases called
eruption columns (분출기둥)
that extends thousands of
meters into the atmosphere.
화산분출 형태
• 요약:
– Fluid basaltic lavas generally produce quiet
eruptions.
• Basaltic flow rates between 10-300m/hour.
• Traveling up to 90 miles (150 km) from the vent.
– Highly viscous lavas (rhyolite:유문암 or
andesite:안산암) produce more explosive
eruptions.
• Rhyolitic lava are much slower.
• Seldom travel more than a few kilometers from
their vents.
화산분출 물질
1. Lava Flows
2. Volatiles
3. Pyroclastic Material
(화산쇄설물)
용암류(Lava Flows)
• Types of Basaltic Flows:
• Pahoehoe
(파호에호에)
lava resembles
a twisted or
ropey texture.
Pahoehoe Lava Flow in
Hawaii Volcanoes
National Park
Pahoehoe
Lava Flow
in Hawaii
Volcanoes
National
Park
Pahoehoe lava flows can contain lava
tubes (용암동굴), cave-like tunnels that
were horizontal conduits for lava.
Lava Tube in Hawaii
Volcanoes National Park
용암류
• Types of Basaltic Flows:
• Aa(아아) lava has a
rough, jagged blocky
texture.
– Cool and thick with gases
escaping forming
numerous voids and
sharp spines.
– Pahoehoe flows are hotter, richer in gases, and
travel faster than aa flows.
– Basaltic lavas can begin as pahoehoe flows and
become aa flows.
용암류
• Types of Basaltic Flows:
– Pillow lavas (베개용암) – lava that
formed underwater.
• Occur along oceanic ridges.
• Lava cools quickly forming
an outer skin.
• Lava advances by breaking
through the outer rind (외피).
• Forms elongated structures
resembling pillows.
Pillow Basalts, Olympic National Park,
Washington
용존가스(Volatiles)
• Magmas contain varying amounts of
dissolved gases held in the molten rock
under confining pressure.
– Consists mainly of:
• water vapor (수증기) and carbon dioxide
(이산화탄소)
– Lesser amounts of:
• nitrogen, sulfur dioxide, chlorine, hydrogen, argon
– Contribute significantly the planet’s atmosphere
(natural air pollution).
– Rise into the atmosphere and may reside there
for years potentially impacting climate.
화산작용과 기후
• Explosive eruptions emit huge quantities
of gases and fine-grained debris into the
atmosphere which
• Filter out and reflect a portion of the
incoming solar radiation.
• This can cause cooling on a global scale.
• Examples of volcanism affecting climate:
• Mount Tambora, Indonesia – 1815
• Krakatau, Indonesia – 1883
• Mount Pinatubo, Philippines – 1991
화성쇄설성 물질(Pyroclastic Materials) –
“Fire Fragments”
• Ash and Dust (화산재) – Fine, glassy
fragments compose tuffs(응회암) and
welded tuffs.
• Pumice(부석) – Porous rock from “frothy”
lava or rhyolitic composition.
• Scoria – Vesicular rock of typically
basaltic composition.
• Cinders – Glassy vesicular fragments 4 32 mm.
화성쇄설성 물질 –
“Fire Fragments”
• Lapilli (화산력)– pyroclastic fragments 2-64 mm in size.
• Particles larger than lapilli:
• Blocks – pyroclasts more
than 64 mm in diameter
ejected in the solid state
(rock torn from the vent
wall).
• Bombs – ejected blob of
hot lava streamlined
during flight (more than
64 mm in diameter).
Bomb is approximately 10 cm long
화산 내부구조
(Anatomy of Volcanoes)
Anatomy of Volcanoes
• General Features
– Magma chamber is connected to the surface by
a conduit or pipe that terminates at a surface
vent.
Anatomy of Volcanoes
• General Features
– Opening at the summit of a volcano:
• Crater – steep-walled, circular depression at the
summit, generally less than 1 km diameter.
– Produced by explosive excavation of rock during eruptions.
• Caldera – a summit depression typically greater than
1 km diameter.
– Produced by collapse following a massive eruption.
Anatomy of Volcanoes
• General Features
– Mature volcanoes develop fissures along the
flanks and base producing parasitic cones and
fumaroles:분기공 (emit only gases and smoke).
화산의 형태와 특징
판구조론과 화성활동
• Global distribution of igneous activity is not random.
• Most volcanoes are located within or near ocean
basins or along continental margins.
• 지판의 경계 형태에 따라 각각 다른 형태의 화성활동
유형을 보인다.
판구조론과 화성활동
• Basaltic igneous activity is common in
both oceanic and continental settings.
• Granitic igneous activity is rarely found
in the oceans.
Not all Volcanoes are the Same
• Factors determining the size
and shape of volcanoes:
1. Volume of lava erupted
2. Viscosity of lava:
• Composition of the magma
• Temperature of the magma
• Dissolved gases in the magma
순상형 화산(Shield Volcanoes)
•
•
•
•
Broad, slightly domed-shaped.
Composed primarily of basaltic lava.
Generally cover large areas.
Produced by mild eruptions of large volumes of lava.
Mauna Loa
Shield Volcanoes
• Most grow up from the seafloor to form islands or sea
mounts.
• From ocean floor to summit, Mauna Loa is over 10,000m
high (higher than Mt. Everest [~8,800m]).
• Large steep-walled calderas occupy the summit.
• Mature volcanoes erupt lava from the summit and rift
zones that develop along the slopes (flank).
Cinder
Cones
(분석구) Haleakala
Maui
• During late stages, shield
volcanoes produce clusters of
cinder cones in summit area.
Shield Volcanoes
and Plate Tectonics
• Shield volcanoes are a product
of intra-plate volcanism in
oceanic crust.
– Activity within a tectonic plate.
– Associated with plumes of heat
upwelling in the mantle – mantle
plume.
– Form localized volcanic regions
in the overriding plate called a
hot spot.
– Produces basaltic magmas
creating:
• Shield volcanoes
• Volcanic chains and seamounts
Volcanism on a
Tectonic Plate
Moving over a
Hot Spot
Produces Shield
Volcanoes
(basaltic) and
Volcanic Island
and Seamount
Chains
Global distribution of flood basalt provinces (black) and associated hotspots (red dots). Red dashed lines are hot spot tracks, which appear as lines
of volcanic structures on the ocean floor. The Keweenawan and Siberian
Traps formed in failed continental rifts where the crust had been greatly
thinned. Whether there is a connection between the Columbia River basalts
and the Yellowstone hot spot is still a matter of ongoing research.
분석구 화산(Cinder Cone Volcanoes)
Sunset Crater – a Cinder Cone
near Flagstaff, Arizona
• Built from ejected lava
fragments – pyroclastic
cinders or clinkers (glassy
vesicular fragments).
• Fragments range in size
from ash to bombs,
primarily lapilli.
• Product of gas-rich basaltic
magma (scoria).
• Steep slope angle.
• Rather small size.
• Frequently occur in groups.
Parasitic Cinder Cones, Mauna Kea, Hawaii
Late-Stage Cinder
Cones, Mauna Kea
Summit, Hawaii
Cinder Cone Volcanoes and
Plate Tectonics
• Cinder cone volcanoes are the product of latestage volcanism in various tectonic
environments.
– Basaltic magmas:
• Associated with hot spot volcanism in oceanic crust:
– Shield Volcano Flanks and Calderas
• Associated with hot spot volcanism in continental crust:
– Flanks of Calderas
• Associated with subduction zones between oceanic-oceanic
crust and oceanic-continental crust:
– Stratovolcano Flanks and Calderas
복합(성층)화산(Composite or Stratovolcanoes)
• Large, classic-shaped volcano (1000’s of feet high &
several miles wide at base).
• Composed of interbedded lava flows and layers of
pyroclastic debris.
• Primarily andesitic in composition with lesser basaltic
and rhyolitic lavas.
Composite or Stratovolcanoes
• Explosive eruptions that eject huge quantities of
pyroclastic material.
• Most are located adjacent to the Pacific Ocean
(e.g., Fujiyama, Mt. St. Helens).
Mt. St. Helens
Mt. St.
Helens
1980
Eruption
Mt. St. Helens Following
the 1980 Eruption